Heat waves at pre-anthesis, post-anthesis, and sequentially across both stages on wheat yield under field conditions.

We investigated the plasticity of grain yield (GY) responses to heat waves (HW) in two genotypes and two developmental stages. Results showed that GY penalties were primarily driven by the intensity of HW rather than genetic background, as genotypic responses to HW treatments were largely similar. Both genotypes exhibited comparable GY penalties, which were associated with similar changes in yield components, despite their contrasting strategies for yield formation. The indirect effects of pre-anthesis (pre-ANT) HW were more pronounced in the genotype relying on average grain weight (AGW; Pistolo), whereas direct effects were more critical in the genotype dependent on grain number (GN; Sublim). Across experiments, HW consistently reduced GY through decreases in GN when applied pre-ANT (but through affecting more grain abortion than floret fertility) and in AGW when applied post-anthesis (post-ANT). When GY penalties were normalized by HW intensity, crops were more sensitive during grain number determination than during grain filling. Additionally, the interaction between sequential HW events revealed an antagonistic interaction reflecting a "priming" effect of pre-ANT HW on the penalty imposed by a post-ANT HW. This antagonism highlights the importance of considering multiple heat stress events when predicting yield penalties under future climate scenarios.